The present invention relates to a sliding bearing which can be used in engine for automobile and other industrial machines.
A sliding bearing for automobile engine is normally made of aluminum alloy or Cuxe2x80x94Pb alloy overlaid by Pb-based material. In recent years, automobile engines having a remarkably enhanced performance such as higher output and higher rotary speed have been developed. Thus, the excellent appearance of a sliding bearing in sliding properties, particularly initial conformability and seizure resistance, as well as in durability and heat resistance has been desired.
JP-A-04-83914 discloses a sliding bearing material having a coating layer comprising a solid lubricant of 55 to 95% by weight and a polyimide-based binder of 10 to 45% by weight, and formed on the surface of an aluminum alloy bearing. Such a solid lubricant layer makes it possible to improve the initial conformability of the aluminum alloy bearing and hence attain an excellent fatigue resistance and seizure resistance. The above mentioned publication discloses that the abrasion resistance of the solid lubricant layer can be improved due to the replacement of the solid lubricant of 1 to 20% by weight by a friction adjustor.
Further, JP-A-07-247493 discloses an incorporation of a film-forming coadjuvant in a solid lubricant layer comprising a solid lubricant of 70 to 97% by weight and a binder (polyimide resin, epoxy resin, phenolic resin) of 3 to 30% by weight. The incorporation makes the solid lubricant be firmly retained on the bearing alloy, provides a good initial conformability and hence an excellent seizure resistance and prevents exfoliation of the solid lubricant layer to give a good abrasion resistance.
However, since the foregoing solid lubricant layer in the related art has an additional amount of a solid lubricant of 55 to 97% or more by weight, an internal strength of coating layer and retention of solid lubricant are insufficient. Accordingly, the conformability deteriorates and seizure or the like occurres due to the exfoliation of the film or other defects cause.
An object of the present invention is to provide a sliding bearing having an excellent initial conformability and seizure resistance as well as desired durability and heat resistance required particularly for high speed engine.
In accordance with the present invention, a sliding bearing having the following constitution can be provided to accomplish the foregoing object of the present invention.
1. A sliding bearing comprising a resin coating layer formed on a bearing alloy layer, wherein that the resin coating layer comprises: a thermosetting resin being soft and having a good elongation at high temperature which exhibits a tensile strength of from 70 to 110 MPa and an elongation of from 7 to 20% at 25xc2x0 C. and a tensile strength of not lower than 15 MPa and an elongation of not lower than 20% at 200xc2x0 C. in an amount of from 70 to 30 vol-%; and a solid lubricant in an amount of from 30 to 70 vol-%, and wherein a bipartite total of the soft thermosetting resin and the solid lubricant becomes 100 vol-%, and a Vickers hardness Hv of the resin coating layer is not greater than 20.
2. The sliding bearing as set forth in above 1., wherein the thermosetting resin is a polyamideimide resin.
3. The sliding bearing as set forth in above 1. or 2., which is used for an internal combustion engine.
In order to improve the initial conformability and the seizure resistance at a high speed, it is necessary to secure a desired thickness of a fluid film by an abrasion or a deformation of the resin coating layer, when the thickness of the lubricant film becomes thin locally or a solid contact comes close to occur.
Heretofore, this demand is coped with by increasing the amount of the solid lubricant. However, when the amount of the solid lubricant is increased too much, the resin coating layer becomes brittle, the exfoliation of the solid lubricant or other defects cause the sliding bearing to undergo easily seizure and thus the a resin coating layer have a deteriorated initial conformability.
Under these circumstances, the inventors have noticed the resin binding the solid lubricant. By using as such a resin a soft thermosetting resin which exhibits a good elongation at high temperature, a sliding bearing having a solid lubricant resin coating layer having a good initial conformability and seizure resistance as well as a good heat resistance and durability was developed. The present invention has thus been worked out.